This invention relates to detecting acoustic energy and in particular fetal heart monitoring.
Fetal heart monitoring is a diagnostic tool to indicate the overall health status of a fetus. Currently deployed fetal heart monitoring techniques are primarily ultrasound, Doppler-based. With a typical ultrasound Doppler-based technique, wires are deployed between an ultra sound transducer unit and processing unit. A skilled operator, such as a medical technician or nurse scans or places a transceiver on the abdomen of the patient. Typically, the operator covers a region on the abdomen with a gel and moves the ultrasonic sensor around the area to scan the area. Alternatively, the sensor can be affixed with a belt that is worn around the woman. The belt is cumbersome and inaccurate (often the sensor slips off of its target) and it has to be removed prior to any surgery or emergency procedure. Acoustic signals are emitted from the transducers and their echo signals are detected by the transceiver and processed to produce data pertaining to the fetal heart rate.
Current Doppler-based techniques for fetal monitoring have several limitations. One limitation of current Doppler-based techniques is the lack of specificity for detecting fetal heart tones (FHT's). In cases of maternal tachycardia, the operator may not be able to differentiate whether the transducer is detecting the fetal or maternal signal, and this can have catastrophic consequences.
Other limitations pertain to changes in fetal position or station which often require re-positioning of the transducer, which can be time-consuming and result in “blackout” periods in fetal monitoring, during which medical personnel do not receive data from monitors that monitor the fetus. Another limitation is the loss of continuous monitoring in a distressed fetus, especially during transition periods, e.g., moving from a delivery room to an operating room for an emergency Cesarean section procedure. In addition, many hospital protocols require detachment of all wires from fetal monitoring devices during room transfers. Detaching fetal monitors begins another “blackout period.”
Administration of epidural anesthesia presents another potential “blackout” period for fetal monitoring, as the transducer is frequently removed or displaced during that procedure. This, too, is a critical time frame for fetal monitoring, as epidural anesthesia may cause maternal hypotension with subsequent fetal bradycardia.
Maternal ambulation has been shown to facilitate labor progress, but current techniques typically preclude such standing deliveries.
A newer monitoring technique known as fetal phonography uses a passive acoustic sensor to capture acoustic energy from the maternal abdomen. Typically, the sensor includes a piezoelectric element. In a paper entitled “Development of a Piezopolymer Pressure Sensor for a Portable Fetal Heart Rate Monitor” by Allan J. Zuckenvar et al., IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING. VOL. 40, NO. 9. SEPTEMBER 1993 p. 963, the authors described a pressure sensor array mounted on a belt worn by the mother. The sensor array uses two polyvinyldene fluoride elements arranged in a bimorph structure, mechanically in series and electrically in parallel.